1. Field of the Invention
The present invention relates to a power-supply device where, independently of a power LC smoothing filter, a signal is caused to pass through a CR smoothing filter and is then fed back so that the control loop will be stabilized.
2. Description of the Related Art
A prior art on the loop stabilizing method for a power-supply device has been described in xe2x80x9cLow-Voltage On-Board DC/DC Modules for Next Generations of Data Processing Circuitsxe2x80x9d, Zhang et al., IEEE Tran. on Power Elect. Vol. 11, No. 2, March 1996. In the power-supply device according to the prior art, a signal is fed back to an error amplifier from a power LC smoothing filter. Then, the error amplifier compensates the phase, thereby implementing the stabilization of the control loop. In this prior art, an aluminum electrolytic capacitor is used as the power LC smoothing filter.
U.S. Pat. No. 5,877,611 discloses a power supply system in which an output of a CR smoothing filter connected across an inductor of an output LC smoothing filter is fed back to an error amplifier having a low input impedance. In the U.S. patent prior art, voltage and current signals of a power supply output are extracted using the CR smoothing filter, so that the resistance value of the CR smoothing filter must be set to be small. The component constants of the CR smoothing filter are a capacitance of 0.47 xcexcF and a resistance of 100 xcexa9. Accordingly, the CR smoothing filter having such constants cannot be formed on chip in a power supply IC and must be formed externally of the IC chip, resulting in a problem that the power supply device cannot be made in small size totally.
In order to downsize the power-supply device, instead of using the aluminum electrolytic capacitor as the power LC smoothing filter, there has occurred a necessity for using a ceramic capacitor of a chip-part as the power LC smoothing filter. However, the equivalent series resistance (ESR) of the chip ceramic capacitor is equal to several mxcexa9, which is considerably small. What is more, the ceramic capacitors are connected in parallel under an actual use condition. Accordingly, the total of the ESRs in this case becomes less than 1 mxcexa9, which is even smaller. This makes it impossible to expect the damping of the ESR as is expected in the case of using the aluminum electrolytic capacitor. Consequently, it becomes difficult to stabilize the control loop.
In the above-described prior art, when using the ceramic capacitor with the small ESR as the power LC smoothing filter, it becomes impossible to expect the damping effect of the ESR. This causes a signal to oscillate, thereby making the phase compensation difficult. Also, if, in the prior art, it were to become possible to implement the phase compensation by narrowing the operation bandwidth of the error amplifier, a response from the power-supply is delayed exceedingly. Moreover, in modifying the LC smoothing filter""s constants, there exists a troublesome task of adjusting the phase compensation condition of the error amplifier on each that occasion.
It is an object of the present invention to provide a power-supply device that employs a novel control method where, independently of a power LC smoothing filter, a signal is caused to pass through a CR smoothing filter and is then fed back so that the control loop will be stabilized.
A power-supply device according to one aspect of the present invention is as follows: In the control loop of the power-supply device of a step-down type DCxe2x80x94DC converter, a CR smoothing filter is provided independently of a power LC smoothing filter. Moreover, a signal corresponding to the output power is fed back to an error amplifier after having passed through the CR smoothing filter.
Also, a power-supply device according to another aspect of the present invention includes the following unit: Independently of the duty controls over Power MOSFETs, i.e., upper-side/lower-side semiconductor switching components in the steady state, the unit adds the output from a power LC smoothing filter to an upper and lower limit value detecting circuit, thereby, at the transient state, forcefully setting the duty at either 0% or 100%.
Moreover, a power-supply device according to still another aspect of the present invention is as follows: The power-supply device includes power-supply device units prepared in plural number. In order to perform a parallel operation of these power-supply device units, the power-supply device further includes an oscillator and a phase shift circuit that the plural power-supply device units have in common. Furthermore, in the steady state, phases of driving pulses of upper-side/lower-side Power MOSFETs in the respective power-supply device units are respectively shifted to phases that result from dividing 360xc2x0 by the number of the parallelism. At the transient state, all of the parallel power-supply device units are operated by driving pulses of one and the same phase.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.